This invention relates generally to the art of measuring gas transmission through solid material and more particularly to an apparatus for quantitatively measuring gas transmission through films and membranes.
In many areas of technology, it is highly desirable to know in advance the gas transmission rate through the various films and membranes. In the packaging industry in particular and in the art of food packaging, as well as in the containment of most biological and phaseological materials, it is highly important to utilize materials which will not permit the permeation of atmospheric gases which will deleteriously affect the packaged substance. Various substances are affected differently by differing gases.
Food products and meats in particular are better preserved in the absence of oxygen. It is thus important that packaging materials be utilized which have a very low rate of transmission for atmospheric oxygen. Other products may be deleteriously affected by the presence of carbon monoxide or carbon dioxide. In any event in order to appropriately select packaging materials, it is necessary that gas transmission rates of interest be known and thus capable of measurement.
Prior to the invention disclosed herein, such measurements have been performed on packaging films within laboratories on a largely manual basis, wherein closed volumes were separated from one another by a film sample. One closed containment volume would either be continuously flushed with and/or closed with the gas whose transmission rate was being measured while the other chamber would contain an inert or carrier gas. At specified periods of time the carrier gas side would be connected to varying types of measuring means to detect the quantity of transmitted gas therein. This measurement process would be repeated on the same sample and on varying samples for varying periods of time until some reproduceability was achieved. This process, however, is manually performed and thus is highly dependent upon the skill of the operator in that precise timing is required for the manipulation of valves and measuring equipment. Additional variables related to the manual operation are the placement of the sample between the two volumes and the detection equipment utilized for detecting the presence of the transmitted gas.
Frequently laboratory arrangements such as that described above are capable of detecting only the presence of a single transmitted gas and would thus not be useful for detecting the presence of any other gas.